Pocket Universes: Gotta Catch ‘em all?

Within popular science, cosmic inflation is a highly discussed and rather popular topic. Why not? It basically explains why the universe looks the way it does, right? Well, that really depends on who you ask. Instead of going into a long discussion on inflation today, I decided to sum up almost every lecture on inflationary pocket universes I’ve been to with series of sarcastic Pokémon-themed panels (Why, Pokémon, you ask? You clearly haven’t been to enough lectures on “Pocket Universes”).

The universe started out very, very small. There is very little reason to doubt that this is a true statement – both theory (just wait for the post/paper that is coming on this) and experiment strongly suggest that there was some type of Big Bang at the beginning of the universe. The universe is rather large now. There is also very little reason to doubt this, although “how large” is still a valid and exciting question (also be excited for the “small universe” posts that will be coming).

So, we know we started small and now we are much larger. Obviously, there has to be some function to map “tiny, early universe” into “large, current universe”. In the broadest sense, we call this function “inflation”. Beyond that, ie. the existence of some process that took the very small early universe into the one that we see today (via some unusual expansion mechanism when it was young), we don’t know as many things for sure about inflation as many people seem to think we do. Unfortunately, that topic is for another day.

Interesting, but I am afraid the “large” and “small” labels don’t make much sense in a curved spacetime. What we take for a an expansion of space may simply be a redistribution of curvature.

To see what I mean imagine that in the early universe there were many locations with extreme mass-energy concentration (say quasars or black holes, but it could be anything) and therefore extreme local curvature and an almost completely empty and flat space in-between them. Now imagine that during the billions of years those quasars and black holes ejected and evaporated most of their mass-energy spreading it almost isotropically throughout the previously empty voids of space as particles and radiation.

To some observers located far from the strong curvature centers it would seem that the space itself expanded with time. But if they could know the total curvature they would realize that a total amount of space did not change, it only got redistributed more evenly throughout the Universe.

To me this is the most likely reason we see universe “expand.” Is there any reason to exclude this explanation?